There is a growing need in the field of touchscreen devices to enable user interaction with the touchscreen device in such a way that subtle variations in the tilt, angle, and pressure of an input device are recognized by the system without adding complexity and costs to the input device itself. The input device is typically a stylus tool. Stylus design is generally broken down into two categories: active and passive. Active stylus design requires additional active (powered) electronic circuitry within the stylus. Passive stylus tools do not have such powered electronic circuitry and are of a simpler design.
Some prior art input devices, such as accelerometer or position based styluses, and digital pens, are only capable of binary input, e.g., the detection system is only capable of recognizing the mere presence or absence of input. These prior art devices are incapable of detecting variations in the tilt, angle, and pressure of the stylus relative to the touchscreen surface.
One prior art approach requires a special flat panel detection layer integrated within the display unit to sense the stylus. The special detection layer is able to detect the position of the stylus, with the stylus having an active transmitter that electronically interfaces with the layer. This approach requires an active stylus, e.g., one that has active and powered circuitry for interfacing with the special touch sensitive layer. The requirement of a special flat panel detection layer and the requirement of having an active stylus both add cost and complexity to this approach.
Other digital pens have relied on accelerometers or Bluetooth communication between devices to detect the presence and position of input from the digital pen. These approaches require an active stylus. While some of these devices are capable of detecting variations in pressure applied using the stylus, such implementations are complex and cannot accurately detect variations in the angle and tilt of the input device. This result is achieved by detecting pressure at the input device itself, rather than detecting pressure at the touchscreen. These implementations also require that the input device and touchscreen device are in constant communication, typically over Bluetooth (or some other radio pathway), which adds device complexity and strains device battery life.
Other prior art solutions include camera based pens which use special digital paper featuring a non-uniform dot pattern printed on the surface. As the camera detects the position of the pen relative to the dot pattern, the presence and position of input is determined. However, this implementation requires an expensive and complex electronic pen with a dedicated (active) power source.